<?php
/**
 * 登录验证码
 */
    session_start();
    header("Content-type: image/png");
    $im = @imagecreatetruecolor(50, 20) or die("建立图像失败");
    $background_color = imagecolorallocate($im, 255, 255, 255);
    imagefill($im,0,0,$background_color);
    $border_color = imagecolorallocate($im,200,200,200);
    imagerectangle($im,0,0,49,19,$border_color);
    for($i=2;$i<18;$i++){
        $line_color = imagecolorallocate($im,rand(200,255),rand(200,255),rand(200,255));
        imageline($im,2,$i,47,$i,$line_color);
    }
    $font_size=12;
    $Str[0] = "ABCDEFGHIJKLMNNPQRSTUVWXYZ";
    $Str[1] = "abcdefghijklmnnpqrstuvwxyz";
    $Str[2] = "11234567891234567891123456";
    $imstr[0]["s"] = $Str[rand(0,2)][rand(0,25)];
    $imstr[0]["x"] = rand(2,5);
    $imstr[0]["y"] = rand(1,4);
    $imstr[1]["s"] = $Str[rand(0,2)][rand(0,25)];
    $imstr[1]["x"] = $imstr[0]["x"]+$font_size-1+rand(0,1);
    $imstr[1]["y"] = rand(1,3);
    $imstr[2]["s"] = $Str[rand(0,2)][rand(0,25)];
    $imstr[2]["x"] = $imstr[1]["x"]+$font_size-1+rand(0,1);
    $imstr[2]["y"] = rand(1,4);
    $imstr[3]["s"] = $Str[rand(0,2)][rand(0,25)];
    $imstr[3]["x"] = $imstr[2]["x"]+$font_size-1+rand(0,1);
    $imstr[3]["y"] = rand(1,3);
    for($i=0;$i<4;$i++){
        $text_color = imagecolorallocate($im,rand(50,180),rand(50,180),rand(50,180));
        imagechar($im,$font_size,$imstr[$i]["x"],$imstr[$i]["y"],$imstr[$i]["s"],$text_color);
    }
    imagepng($im);
    imagedestroy($im);
    $_SESSION['verification_code']=strtolower($imstr[0]["s"].$imstr[1]["s"].$imstr[2]["s"].$imstr[3]["s"]);
?>